One place to start would be to ask your HS track coach for some advice, especially about running form. A lot of baseball players have horrible form (including me at one point), mostly because they were never taught how to run. Focus on a quick first step. Ask about flexibility work...hurdle workouts are great, bounding and dynamic stretching are great as well (done correctly). Next, strength training is a must. Focus on squats/variations, deadlifts, powercleans/variations, and other explosive exercises. World class sprinters can typically squat 500+ for reps. Personally I've always been fast but after I worked with a track coach this winter I got a lot better...if you can, run indoor track in the winter (55m, 4x200, long jump, etc). It's pretty fun and great for baseball conditioning.
Good luck!